This invention relates to an improvement of an ophthalmological photographing instrument which has irradiation means for irradiating illuminating light to the fundus of an eye to be tested, projection means for projecting a target luminous flux to the fundus of the eye, and image receiving means for receiving a reflection image of a target image luminous flux reflected by the eye together with an image of the fundus of the eye, and in which, based on output of the images received by the image receiving means, the eye is observed/photographed and the eye can be photographed under a fluorescent light.
Heretofore, there are known as recording systems which can be employed in an ophthalmological instrument, a still image recording system using a film and an electronic picture recording device as recording media, and a moving image recording system using an electronic picture recording device (for example, VTR or the like) as a recording medium. There are known, as photographing systems which can be employed in an ophthalmological instrument, a visible color photographing system, a visible fluorescent light photographing system, an infrared fluorescent light photographing system and the like. The fluorescent photographing technology is utilized for a diagnostic check of a circulating state of blood flowing in the blood vessels of the eye fundus. As one effective recording system for it, the moving image recording system receives much attention. Lately, the moving image recording system has been increasingly employed with the further improvement of the performance of electronic picture recording devices.
The ophthalmological instrument includes, in order to avoid incorrect photograph, an alignment projection system for projecting an alignment target to the eye in order to align the instrument body with the eye, and a focusing projecting system for projecting a split target to the eye fundus, which serves as a target for adjusting a focusing state of the eye fundus.
Those targets are projected to the eye fundus or cornea. Therefore, if an eye fundus image should be received as it is, it could happen that a desired eye fundus part is impossible to be recognized because those target images are transferred together with the eye fundus image and the target images are superimposed on the eye fundus image.
In the case of a still image recording, it is made possible by extinguishing or blocking a target luminous flux only when a recording is carried out that the target image is not transferred when the image of the eye fundus is recorded. However, in the case of a moving image recording, it is practically impossible to extinguish or block the target image luminous flux only when a recording is made because a picture recording is constantly made. Since those target images are transferred together with the eye fundus image, they are superimposed on the eye fundus image. As a consequence, it gives rise to the inconvenience that a desired eye fundus part is impossible to be recognized.
It can be contemplated not to project those target images when a moving image is recorded. However, this is practically impossible to be applied to the case of a fluorescent photograph, because when a fluorescent photograph is made, a fluorescent eye fundus image is unobtainable for a time interval from a few seconds to a few dozens of seconds which are required for a fluorescent agent to reach the blood vessels in the eye fundus and the examiner is compelled to observe the eye fundus in the dark during that time interval. As a consequence, it is impossible to recognize whether or not the instrument body is correctly aligned with the eye and whether or not the eye fundus image is well focused. It is only after the fluorescent eye fundus image is obtained that the incorrect alignment and incorrect focusing are confirmed. Thus, there is a fear that an attempt to photograph an initial fluoresent fundus image is failed.